Electronic power generation



A 1948. s. LAPPIN ETAL 2,447,616

' ELECTRONIC POWER GENERATION Filed April '7, 1945 ATTORNEY PatentedAug. 24, 1948 Lester S. Lappin, Camden, and Robert'F. Holt z,

Merchantville. N. J., assignors to Radio Corporation of America, acorporation of Delaware Application April 7 1945, Serial No. 587,176

This application discloses a new and improved means for generating highfrequency power.

A general object of the present invention is to improve high frequencypower generators for industrial and similar purposes.

A more particular broad object of the present invention is improvedmeans of dielectric heating of non-conducting materials.

Power generators of the nature involved here known in the prior artinclude an electron discharge tube in a regenerative oscillationcircuit. In many instances the regeneration circuit includes a tankcircuit inductance through which the direct current for the tube anodeflows. These power generators are satisfactory in many cases, but are oflimited application for various reasons, many of which flow from thepresence of the direct current and/or voltage in the tank inductance.For example, the tank circuit inductance in many cases is in or adjacentthe load or material being worked on, so that the operator or operatorsare sufficiently near thereto to be endangered by the high voltageand/or currents involved.

Moreover, in many of these known systems inductive coupling between thetank circuit and the load is used, and in many cases these arrangementsoperate unsatisfactorily because this 9 Claims. (c ase-4s) circuitarrangement wherein the direct current is eliminated, thereby reducingthe danger to which the operator is exposed. To attain this object, weprovided a regenerative generator of the Colpitts type with two tubesand a tank circuit wherein blocking and coupling capacity is usedbetween the anodes of the generator tubes and the tank circuit to keepdirect current and voltage out of the tank circuit. l

A further object of the invention is to provide a radio frequency powergenerator suitable for wide use in the industrial heating art, and one Iirrespective of thenature of the material orload sort of coupling to theload causes trouble of various natures. For example, a phenomenon knownas frequency skip is often encountered. By this it is meant that theoscillation generator might operate intermittently atits operatingfrequency and shift erratically to other frequen-. cies not satisfactoryfor the use at hand.- Furthermore, where inductive coupling is used onloads of certain material fullpower output is unattainable. This mayoccur where the dielectric load is of low power factor or where loads ofhigh impedance are being worked on or big masses are adjacent the outputbushings or'terminals of the system. Thus in many. known systems theoperators are exposed to the-high direct current potentials and voltagesof; thebeing worked on. To attain this object we provided a directcoupling or shunt feed from the tank. to the load to eliminate frequencyskip and otheroperational defects of the nature mentioned above. v t va: The blocking capacities available for couplin g the anodes to thetank circuit blow up or burn outbecause-of capacity limitations at highfrequency. In other words, there are notavailable condensers which willcarry the load involved satisfactorily. To overcome'this limitation weuse two condensers'in parallelas blocking condensers between'the anodesof the tube and the tank circuit. Then due to lack of uniformity incondenser manufacturing we found that the division of current and powerthrough the blocking condenser would become unequal and again one of thecondensers would fail throwing the entire load on the remainingcondenser which would also fail; This unequal distribution or divisionof current in the condensers takes place and is believed to be due tovariations in the condenser characteristics and structure, some of whichvariations are as follows. One condenser may have more ,ca-.pacity-reactancethan the other-so that-there is a tendency for onecondenser to carry more than its share of the load. Another causemayresult from the fact that in one condenser the inductive reactancemay almostequal the capacitive reactance so that this condenser is ofsubstantially zero impedance to the high frequency power being suppliedto the tank and this condenser assumes more of the, load than the other,and since its arrangement and {dimensions are in general the sameas theother it heats up or fails otherwise,

To overcome the above defects we include in series with the two blockingcondensers inductive reactance which is large as compared to thereactance of the condensers. This inductive reactance then provides sucha large part of the total reactance of the parallel connections that anyinequalities in the reactances of the two condensers are swamped out andare ineffective to cause one of the condensers to assume more than itsshare of the load.

The power generator of the present invention is to operate at variousfrequencies. intheembodiment tested and found highly satisfactory thegenerator operates at 2, 5 and megacycles. To facilitate this operationa novel arrangement of tank circuit tuning condensers has been providedwhich permits ready adjustment of the tank circuit tuning to the severalfrequencies at which it is desired to operate.

Although it is believed that our invention will be understood from thedescription given above, a detailed description of the manner in whichour objects are attained and the advantages derived.

therefrom will now be given. In this description, reference will be madeto the attached drawings whereinthe singlefigure illustrates theessential elements of a power generator arranged in accordance with ourinvention. The circuit diagram of the drawings is basicand'it willbeobvi-ous to those skilled inthe-ar't that the practical embodimentwhich we found highly satisfactory includes many refinementsandoperating circuit elements not shown, being not'a part of the" subjectmatter claimed. For example, in the drawings the metering circuits,control circuits, electrode'sup ply rectifier circuits, and filamentheating" circuits, or portions thereof at least, are omitted. Y lnthedrawings two electron discharge devices VI' and V2 have their controlgrids and'anodes coup ed in a parallel circuit. of the Colpitttype fortheproduction of radio frequency power by regenerative generation ofoscillations. The grids of the two tubes are coupled together byparasitic damping impedances including inductances'Ll and L2shunted'byresistors RI and R2. The anodes are tied together andconnected by the blocking condensers O8 and C9- to theterminals of aninductance' L3, a point of which is connected to one-end of the tankcircuit inductance L4. The othenend of theinductance L4 is coupled (inthe switch position shown) by condensers C'G to a point intermediateparasitic damping .inductances and resistances LIRI, L2R2. A point onthetankinductance L4 is coupled by a choking inductance L5 to ground,thus preventingthe accumulation of a static charge in the tank coil,providing additional protection to the operator. Direct current for theanodecircuits of the tubes VI and V2 is supplied from a source not shownby way of a radio frequency choke RFC connecting the anodes to aposmvetermmm on the source, the negative terminal of which is conhectedto'giound and to the cathode of tube V! b'y resistorR3 and resistor R4and to the cathode of V2" by resistor R3 and R5. The direct current grid circuit includes radio frequency choke L6, resistance-R6 and abranch Rlto the cathode of tube vl andabranch R5 to the cathode -of tubeV2. 'Thbias results from tube current through the" gri resistance R6.-A'inetei' Ml denotes the grid current intensity.- The cathodes may beheated by alternating current supplied through transformers T2 and TI.Qscillations are generatedby virtue of the fact that the tank circuitterminus connected to-the' anodesandgnds o reactanceof C8 and cs in anembodiment which proves satisfactory, is 8 ohms and the inductivereactances (external and internal) are comparable to the capacitivereactance resulting in an extremely low net reactance. If the strayinductive reactances of the two capacitors are not equal the net.un'balance may be relatively great resulting ina considerable currentunbalance and overheating of C8 or C9. The balance coil L3 is connectedin series with each capacitor and the mutual inductance thereof is ofsuch a magnitudethat its reactance in each branch is large as comparedto the stray inductive reactances and variations in the stray reactanceshave relativly-sinall effect with respect to unbalancing thecurrentsthrough the two condensers.

Th load or output circuit including the leads 2t and the output plugs26, is directly coupled to the tank inductance L4 so that frequencyinstability (frequency skip or jumping) is held to a minimum in allcases including the case where the output works on a load of low powerfactor.

As stated above the power generator is to oper'ate at severalfrequencies, in the embodiment developed at'frequ'encies of 2, 5 and 10megacy'cles'. To permit such operation an improved tank circuit isprovided. The tank circuit comprises inaddition to the capacity withinthe tubes between the plate and cathode, etc, and between theplates andground, the inductance L4 and condenser C2, the COIIdIISGlSC5, C6 andC'B.

For high frequency operation (10 megacycles in the; present embodiment)the plate end of the tankcircuit istuned by the tube internal capacityand the stray capacitive between plates and ground, etc, and M. For lowand medium frequency operation condenser C2 is added byconnecting thesame betweenthe plates and cathode. The'g rid capacity for the highfrequency operation (lomegacycles) includes in addition to the capacityin the tube between the grid and cathode the variable condenser C5 andthe fixed condenser C6. 'Then the condenser CB is the grid blocking(coupling) condenser through which the feedback takes place. Forthe lowand medium frequency ope-ration condenser CB is put in shunt with C6and-o5 and condenser C! is switched in as the grid coupling condenser..The choke coils RFC andILG are changed to a value appropriate foreacl'ioperating' frequency. The condenser C5 is such-that withqCficonnected in parallel thereto and C2 out of'the circuit the tank may betuned to the highest frequency, i.e., 10 megacycles, with G21 includedin-the plate end of the circuit and G6 in-shunt'with C6 and C5, with C1acting as the-coupling condenser the tank circuit may be tuned to themedium or lowoperating frequencies, i.e., ,2"or 5 megacycles. Althoughit will be readily understood that the circuit element dimensionsand-values depend on the operating frequencies and that my invention isnot limited to particular circuit element dimensions and values, in oneembodiment which operated very satisfactorily the-circuit elements wereas follows:

The tubes and V2 are type RCA892R.

RI=100 ohms R2=100 ohms R3=0.2 ohm R6=2560 ohms Ll=1 turn 2" dia. atmc., 2 turns 2" dia. at

2 and 5 mc.

L2=1 turn 2" dia. at 10 mc., 2 turns 2" dia. at

2 and 5 mc.

L3=5 turns 1 /2" dia. approx.

L4=to tune to appropriate frequency with given capacity L6=self-resonantat approx. operating frequency C2=.0004 microfarads approx.

05:.00056 microfarads C6=500 microfarads approx.

C6=625 microfarads approx.

C'!=.003 microfarad C8=.0D2 microfarad 09:.002 microfarad What isclaimed is:

1. In apparatus for electronically generating oscillatory power forindustrial and like purposes, an electron discharge device having ananode, a cathode and a control grid, coupled in regenerative circuitincluding inductive reactance and capacitive reactance in parallel, theparallel reactances being coupled at one end to the anode of the deviceand at the other end by feedback coupling to the control grid of thedevice, direct current blocking condensers connected in parallel in thecoupling between the anode of the device and said one end of saidparallel reactances, and. means for equalizing the current through thesaid blocking condensers comprising conductors coupled by mutualinductance in series with the parallel blocking condensers. 2. Inapparatus for electronically generating oscillatory power for industrialand like purposes, an electron discharge device having an anode, acathode and a control grid, coupled in regenerative circuit includinginductive reactance and capacitive reactance in parallel, the parallelreactances being coupled at one end to the anode of the device and atthe other end by feedback coupling to the control grid of the device,direct current blocking condensers connected in parallel in the couplingbetween the anode of the device and said one end of said parallelreactances, and means for equalizing the current through the saidblocking condensers comprising a winding in series with each of saidblocking condensers.

3. In apparatus for electronically generating oscillatory power forindustrial and like purposes, a plurality of electron discharge tubeseach having an anode, a cathode and a control grid parallel coupled in aregenerative circuit including a tank circuit having inductive reactanceand capacitive reactance in parallel, the parallel reactances beingcoupled at one end to the anodes of the tubes and at the other end byfeedback coupling to the control grids of the tubes, direct currentblocking condensers connected in parallel in the coupling between theanodes of the tubes and. said one end of said parallel reactances, andmeans for equalizing the current through the said blocking condensersincluding a winding in series between adjacent ends of the parallelblocking condensers so that each blocking condenser has a portion ofsaid inductance in series therewith in the parallel connection.

4. In apparatus for generating oscillatory power for industrialpurposes, an electron discharge device havingan anode, a cathode, and acontrol grid, coupled in a Colpittscircuitincluding parallel inductanceand capacity coupled at one end to the anode and at the other end byfeedback connection to the control grid, direct current blockingcondensers in the connection between the anode and said one end of saidtank circuit, and means for equalizing the current through the saidcondensers comprising a balancing inductance coupling the tank endterminals of said condensers together with a point on the balancinginductance connected to said one end of said tank circuit.

5. In apparatus for generating power for industrial purposes, anoscillation generator of the Colpitts type comprising at least oneelectron discharge tube having an anode, a cathode and a control grid, atank circuit connected by parallel blocking condensers to the anode ofsaid tube and by a feedback condenser to the control grid of said tube,the purpose of said blocking condensers being to prevent direct currentfrom flowing in said tank circuit and to feed oscillatory power from thetube to the tank circuit, and means for preventing unbalanced reactanceof the parallel condensers from causing failure of one thereof includinginductance in parallel between the tank terminal ends of said blockingcondensers and said tank circuit.

6. Apparatus for generating oscillatory power for industrial and likepurposes, at least one electron discharge tube having an anode, acathode, and a control grid, a parallel tank circuit comprisinginductance and at least the capacity inherent between the tubeelectrodes, a connection between a point on the inductance of said tankcircuit and the cathode of said tube, a connection between one terminalof the tank circuit and the anode of the tube, a feedback couplingbetween the other terminal of the tank circuit and the control grid ofthe tube whereby oscillatory energy is developed in the tube when theelectrodes thereof are energized, means for blocking the flow of directcurrent in said tank circuit when the electrodes are energized includinga pair of condensers each having a terminal tied together and to theanodes of said tubes, and a blocking condenser reactance balancinginductance connected at its terminals to the other terminals of saidblocking condensers and at a point intermediate its terminals to thesaid one end of tank circuit.

'7. In an oscillatory power generator, an electron discharge devicehaving an anode, a cathode and a control grid, coupled in regenerativecircuit including inductive reactance and capacitive reactance inparallel, the parallel reactances being coupled at one end to the anodeof the device and at the other end by feedback coupling to the controlgrid of the device, direct current blocking condensers connected inparallel in the coupling between the anode of the device and said oneend of said parallel reactances, and means for equalizing the currentthrough the said blocking condensers comprising conductors coupled bymutual inductance in series with the parallel blocking condensers.

8. In combination, a pair of condensers of substantially equal capacity,a connection directly connecting a pair of terminals of said condenserstogether, a coil connected to and between the other terminals of saidcondensers, and conductors connected to said direct connection and tothe midpoint of said coil whereby alternating annexe.

7 current fed from; ones conductor to; the other-does not: produceharmful .unequak current flow through said condensera.

9: In; apparatus for generating powen for in? dustrial purposes,v an;election dischargedevice having an. anode; a cathode: and a controlgrid, ci-ncuits: including: a tankz'cincuit coupling the an: ode,cathode and control; grid of said. device in. a regenerative oscillationgenerating circuit; said. tank circuit comprising parallel am inductorand a capacitor inciudi'ngr at least the inherent capacity" betweendevice electrodes,. at source of direct current potential connected:between the anode and cathode of said" device, andmeans for preventingdinec't current potential from. appearmg" in. said tank v circuitincludingy inlthe couplings between thev anode ofi said device and said.tank circuit, a pairof capacitors, said capacitors each having aterminal tied to the anodeoffsaiddevice and a second inductor connectedbetween" the REFERENCES CITED The following references are of recordsinthe file of this patent:

UNITED STATES PATENTS Number Name Date 1,110,550 Hewitt Sept.,15,-19141,946,746 Kemp Feb..13,v1934: 2,001,277 Lewis May- 14, 1935 2,145,124Mead, Jr Jan. 24-, 1939; 2,282,968 Kenefake May 1 2-, 1942 2,288,364McArthur June 30", 19,42

